Today most industrial plants include network communication between various entities in the plant for providing distributed control. The communication is normally carried out by means of a network such as a fieldbus network or an industrial Ethernet network. The fieldbus or industrial Ethernet network links controllable devices in the plant, such as motors, switches, valves etc, and data collecting devices, such as sensors, to programmable logic controllers (PLCs) which in turn are connected to a human machine interface (HMI) where an operator can monitor and control the plant. Examples of different fieldbus technologies are CANopen, DeviceNet, ControlNet, CC-Link, Modbus, INTERBUS, sercos and PROFIBUS. Likewise, many different industrial Ethernet technologies coexist, such as EtherCAT, POWERLINK, EtherNet/IP, Modbus TCP, PROFINET, sercos III and CC-Link IE Field.
Despite the above technologies share the generic names “fieldbus” or “industrial Ethernet” the differences between them may be substantial such that they are not readily interchangeable and may not be easily connected to each other. To this end, the applicant has developed a generic two-port communication module under the name Anybus™ which facilitates the connection of an electric device to various different network types by providing an Anybus™ interface on one of the ports and any fieldbus or industrial Ethernet interface on the other port. The communication module comprises electronic circuitry which translates data communicated between the device and different industrial network protocols such that the device may communicate with other network devices independently of the network used.
The speed on an industrial network may vary considerably. Some network standards, such as LIN (Local Interconnect Network) provides low speed and low cost busses for automotive applications in order to interconnect smart sensors and actuators. The speed (e.g. <20 kbit/s for LIN) on such networks is not a critical aspect and may hence be low. If higher network speeds are required i.a. Profibus may be used which provides speeds up to 12 Mbit/s, and in extremely time-critical real time control applications, a much higher network bandwidth is provided i.a. by EtherCAT and Ethernet/IP which today provide speeds up to 100 Mbit/s. Systems like CC-Link IE Field even uses 1 Gbit/s to obtain required performance and real-time levels.
When a communication module is connected to a high speed fieldbus or industrial Ethernet network, and used together with a device in real time applications, it is of outmost importance that the time delay (latency) in the communication unit is kept at a minimum. That is, the time from reception of data (e.g. a data frame) in the communication unit until the relevant data in the frame is forwarded to the device to which the communication unit is connected must be very short. In some applications the delay, in respect of the transmission of process data, in the communication unit may not exceed 15 μs in order to ensure correct functioning of the device.
FIG. 1 discloses by way of example the architecture of a prior art communication module 100 for use in an industrial network. The Industrial network 110 is connected to a network interface 120 in the communication unit 100. The network interface 120 includes at least portions of what is referred to as layer 1 (physical layer) of the protocol stack according to the seven-layer OSI reference model (sometimes abbreviated to three layers for fieldbuses), and receives signals representing the data frames sent over the industrial network 110. The design of the network interface (connectors, interface electronics etc.) depends on which industrial network the communication module 100 is arranged to be connected to, i.e. various transmission technologies are available, such as wired (e.g. RS485), optical (e.g. fiber cables) and wireless. Upon reception of the signals representing a data frame, the network interface 120 performs layer 1 processing of the signals and sends the data frame (or part of the frame depending on the application) to a data processing unit 130 arranged in the communication unit 100. The data processing unit 130 performs any necessary higher layer processing (normally layer 2) and sends the data, which could relate to process data, parameter data, diagnostic data or the like, to the device 140 (e.g. a motor control). Normally a buffer 150 is used for buffering data to be transmitted/received to/from the device 140, and a device interface 160 is arranged in the communication unit 100 for providing the physical signals to the device 140.
Reference to the above, in order to keep the delay in the communication unit 100, and in any communication equipment in general, at a minimum specialized network processors are normally used for implementing the network interface 120 and the data processing unit 130.